Recent developments of high-brightness light emitting diodes (LED) have opened new horizons in lighting. Highly efficient and reliable LED lighting continuously wins recognition in various areas of general lighting, especially in areas where cost of maintenance is a concern. LEDs are being adopted in a wide variety of electronics applications, for example, architectural lighting, automotive head and tail lights, backlights for liquid crystal display devices including personal computers and high definition TVs, flashlights, etc. Compared to conventional lighting sources such as incandescent lamps and fluorescent lamps, LEDs have significant advantages, including high efficiency, good directionality, color stability, high reliability, long life time, small size, and environmental safety.
Referring to FIG. 1, a prior art LED ballast circuit 100 (hereinafter ballast circuit 100) is shown. The ballast circuit 100 may be used with a linear or switching power supply for powering a string of light emitting diodes (LED) 102 from an input voltage source 101. The ballast circuit 100 includes a regulator element 111, linear or switching, and a control circuit 110, where the control circuit 110 is powered from the voltage that develops across the regulator element 111. A resistor 109 represents total parasitic series resistance. An example of such resistance 109 in a switching regulator is the DC resistance of the magnetic coil. The resistor 109, generally speaking, may also include dynamic impedance of the LED string 102. The minimum voltage dropout across the ballast circuit 100 is therefore limited to the minimum voltage necessary for operation of the control circuit 110.
Therefore, it would be desirable to provide a system and method that overcomes the above.